1. Field of the Invention
The present invention relates to a fluid machine, for example, used for a supercharger of an automotive vehicle.
2. Description of the Related Arts
A Roots displacement compressor 201 as shown in FIGS. 1 and 2 is described in Japanese Patent Unexamined Application Laid Open No. 2-91492.
The compressor 201 is provided with a compressor casing 203, a pair of rotors 205 and 207, an input pulley 209 and a timing gear set 211.
Each of the rotors 205 and 207 is disposed within a rotor chamber 213 provided in the casing 203 and is rotated by a driving force of an engine input through the input pulley 209. The timing gear set 211 rotates each of the rotors 205 and 207 to an opposite direction to each in a synchronous manner in order that each of the rotors 205 and 207 is not brought into contact with each other.
As shown in FIG. 2, a suction port 215 and a discharge port 217 for a fluid is provided at a position substantially perpendicular to an axial direction of each of the rotors 205 and 207 in the casing 203.
The rotor chamber 213 is structured such that a horizontal cross section (a cross section in a direction perpendicular to the axis) is formed as a letter 8 shape by holes 219 and 221 corresponding to a rotating track of a front end of each of the rotors 205 and 207, and convex portions 223 and 225 projecting to each of the rotors 205 and 207 are formed in a crossing portion of each of the holes 219 and 221 along the axial direction of each of the rotors 205 and 207.
However, as shown in FIG. 3, in the casing 203, the discharge port 217 end becomes a high temperature and is expanded, the suction port 215 end having a lower temperature than the discharge port end is compressed, and a heat moves to the low temperature end from the high temperature end as an arrow 227. Due to an expansion, a compression and a heat movement generated in the above manner, the suction port 215 is displaced to an inner side as described by a broken line 229 and the discharge port 217 is displaced to an outer side, so that a distortion is generated in the casing 203.
Further, since a suction air in the suction port 215 end has a pressure lower than that in the discharge port 217 end, each of the rotors 205 and 207 is displaced to the suction port 215 end by this pressure difference. The displacement is generated in such a manner that each of the rotors 205 and 207 swings around a bearing 231 or a bearing 233.
Due to the distortion of the casing 203 and the displacement of each of the rotors 205 and 207, the casing 203 and each of the rotors 205 and 207 are interfered with each other, so that an abrasion, a seizure, a poor motion of the compressor 201 and the like are generated.
Still further, since the convex portions 223 and 225 are formed in the casing 203, there is a risk that the abrasion, the seizure, the poor motion and the like when the casing 203 and each of the rotors 205 and 207 are interfered with each other are promoted.
Furthermore, in the Roots displacement compressor 201, there is a problem that a discharge of a fluid is intermittently performed and a back flow is generated in the discharge end so that a noise is increased.